1. Field of the Invention
The invention concerns an arrangement for the adjustment of the position of a shearbar with respect to the knives of a chopper assembly, for use in a harvesting machine, and a method of adjusting the arrangement.
2. Related Technology
In forage harvesters the spacing between the chopper knives and the shearbar is a significant value for the quality of the cut and the power required for the cutting operation. As a rule, shearbars of this type are arranged so that they can be adjusted with respect to the chopper drum by means of electric motors, where each end of the shearbar is associated with an electric motor. A spacing sensor, that as a rule is configured as a knock sensor or a magnetic spacing sensor, detects a signal that contains information regarding the spacing between the shearbar and the nearest knife of the knives on the chopper drum.
In the state of the art various procedures are known in order to bring the shearbar into the desired position relative to the chopper drum by an automatic control of the electric motors.
EP 0 291 216 A suggests initially moving both ends of the shearbar away from the chopper drum. Then one end of the shearbar is next moved towards the chopper drum, until a sensor detects a contact between the shearbar and the chopper drum. Then this particular end is moved away from the chopper drum by a first distance and the other end of the shearbar is moved towards the chopper drum, until a sensor detects a contact between the shearbar and the chopper drum. Then the other end is again withdrawn from the chopper drum by the first spacing. This procedure is performed successively until both motors bring about a contact between the shearbar and the chopper drum upon their activation. Then the shearbar is retracted from the chopper drum at both ends by a path of from approximately 0.127 to 0.254 mm.
EP 0 335 256 A describes an arrangement in which one end of the shearbar is moved in the direction of the chopper drum by a first motor until a contact exists. Then the shearbar is again retracted by the first motor until no contact exists. Then the other adjusting motor is activated until a contact exists and is activated in the opposite direction until the contact between the shearbar and the chopper drum disappears. This adjusting process is repeated once where after each of the last adjustment steps the desired gap on each side is adjusted by retracting the shearbar.
DE 100 21 659 A proposes that one end of the shearbar be moved at first in the direction of the chopper drum until a contact occurs and then retracting it by a spacing that corresponds to the desired gap. Then the other end is moved to the chopper drum until a contact occurs and then retracted again from the chopper drum by a spacing that corresponds to the desired gap. Alternatively the shearbar is at first brought into a parallel orientation to the chopper drum and then the final spacing is adjusted by moving both ends synchronously. For such an adjusting operation a very precisely-operating spacing sensor is required.
EP 1 080 630 A proposes that one end of the shearbar be moved at first to the chopper drum until an appropriate gap exists. Then the other end is moved to the desired spacing.
Thereby the known procedures for the adjustment of the shearbar relative to the chopper drum always include a step in which a first end of the shearbar is brought into the vicinity of the chopper drum. Following this, the other end of the shearbar is moved to the chopper drum. This procedure is based on the fundamental assumption that the chopper assembly is manufactured and ground as a cylinder or a concave shape. The end of the shearbar that was not moved in each case is located at a relatively small spacing from the chopper assembly, so that the assumption can be made that an approach or a contact between the shearbar and the chopper assembly occurs first at the end of the shearbar that was moved on the basis of the cylindrical or concave shape of the chopper drum. In each case the target position of the shearbar is then determined on the basis of the measured values.
This procedure is problematic if the shape of the chopper assembly is convex. This shape can result, for example, from higher wear in the outer region of the chopper assembly on the basis of greater amounts of crop due to non-uniform supply of crop, in that larger amounts of crop are supplied to the outside of the chopper assembly compared to the supply in the center, or on the basis of grinding processes in which the grinding stone operates for a longer time at the edge than in the center of the chopper assembly.
To illustrate this point, reference is made to FIG. 1. The chopper assembly 22 is convex, where the convexity “a” is shown to an exaggerated degree for purposes of illustration. In actual cases it may amount, for example, to 0.5 mm. at a width of the chopper assembly 22 of approximately 700 to 850 mm. and a diameter of the chopper assembly 22 of approximately 600 mm. Depending on the distance “b” of the end of the shearbar 38 that was not repositioned, the shearbar 38 comes into contact with the knives 48 further towards the edge or in the center of the chopper assembly 22. The spacing “b” between the chopper assembly and the end of the shearbar 38 that was not adjusted is relatively small, so that the contact between the shearbar 38 and the chopper assembly 22 occurs in the vicinity of its center.
In case the spacing “b” between the end of the shearbar 38 that was not repositioned and the chopper assembly 22 differs upon the approach of the other end of the shearbar to the chopper assembly the contact thereby occurs at various different axial positions. In a procedure in which the shearbar is moved towards the chopper assembly in successive alternating steps at both ends, the orientation between the enveloping circle described by the knives and the shearbar depends upon chance, and a parallel orientation is difficult to achieve.
The problem underlying the invention is seen in the need to provide an arrangement for the adjustment of a shearbar, in which a parallel adjustment between the shearbar and the enveloping circle described by the knives is possible even with convex chopper assemblies.